In winding and feeding cables of equipment (a transformer, a motor, a reactor, an induction heating device, a magnetic head device, and the like) conducting high-frequency currents, an eddy current loss occurs inside a conductor due to a magnetic field caused by the high-frequency current. As a result thereof, there are cases where AC resistance (high-frequency resistance) increases, thereby causing an increase of heat generation and electricity consumption.
As a factor causing the AC resistance to increase, there are a proximity effect and a skin effect.
As illustrated in FIGS. 17A and 17B, the proximity effect is a phenomenon in which an eddy current 53 is generated due to an external magnetic flux 54 and current density J is biased inside a conductor 51.
As illustrated in FIGS. 18A and 18B, the skin effect is a phenomenon in which the current density J becomes high near the surface of the conductor 51 when a conductor current 52 flows in the conductor 51. The eddy current 53 is generated due to an internal magnetic flux 55, and a region where currents flow is restricted. Accordingly, AC resistance increases.
As countermeasures for preventing the proximity effect and the skin effect, generally, the diameter of a wire is reduced and a litz wire in which each element wire is subjected to insulation coating is employed (for example, refer to PTL 1 and PTL 2).
FIGS. 19 and 20 illustrate examples of the element wire of the litz wire (refer to PTL 3).
In an insulation-coated copper wire 30 illustrated in FIG. 19, insulation coating 32 is formed on the external surface of a copper wire 31. In an insulation-coated copper wire 40 illustrated in FIG. 20, a magnetic material plating layer 42 and insulation coating 43 are formed on the external surface of a copper wire 41.
As illustrated in FIG. 21, in the insulation-coated copper wire 40, when an external magnetic field 44 is applied, the magnetic field 44 is distributed in the magnetic material plating layer 42 in a biased manner, and the influence of the magnetic field 44 is reduced in the copper wire 41. Therefore, compared to the insulation-coated copper wire 30 (refer to FIG. 19) having no magnetic material plating layer, it is possible to prevent the proximity effect in a copper wire.